<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <meta http-equiv="X-UA-Compatible" content="ie=edge">
  <title>Document</title>
  <style>
    .num {
      width: 400px;
      text-align: center;
      line-height: 240px;
      font-size: 60px;
      background: #f4f3f3;
    }
    button {
      width: 200px;
      background: #c15e00;
      color: #fff;
      font-size: 60px;
      border: none;  
    }
    .js-sub {
      background: #454242;
      margin-left: -5px
    }
  </style>
</head>
<body>
  <div id="calculator">
    <div class="num">{{ val }}元</div>
    <button class="js-add" v-on:click="add(1)">+</button>
    <button class="js-sub" v-on:click="sub(1)">-</button>
  </div>

  <div style="display:none;">
    <img src="./mvvm.png" alt="">
  </div>
  <script src="./vue.js"></script>
  <script src="./app.js"></script>
</body>
</html>